Brick press having density control



Feb. 13, 1968 c. A. scHAcHT PRESS HAVING DENSITY CONTROL 5 Sheets-Sheet l Filed Oct. 24, 1965 Hg; I

INVENTOR.

CHQ/.ES 5% Feb. 13, 1968 c. A. scHAcHT 3,368,254

PRESS HAVING DENSITY CONTROL.

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CHARLES 4. SCHACHT ATTORNEY United States Patent O 3,368,254 BRICK PRESS HAVING DENSITY CONTROL Charles A. Schacht, Pittsburgh, Pa., assignor to Harbison- Walker Refractories Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 24, 1965, Ser. No. 504,762 2 Claims. (Cl. 2S-90) This invention relates to an apparatus for controlling the density of refractory brick made from nonplastic brick-making batches.

In recent years there has been a trend toward making basic refractory shapes from batches containing synthetic materials such as dead burned magnesite and electricallyfused chrome ore-magnesia materials. To realize the full benet of these outstanding raw materials-which are themselves nonplastic-the usual batch plasticizers, such as clay, have been eliminated because they introduce undesirable impurities. The nonplastic character of synthetic raw materials, the absence of plasticizers, and the higher forming pressures that are now being used have introduced new manufacture problems. One such problem, controlling brick pressing to obtain uniform high density, is the subject of this application.

tAn understanding of the operation of a toggle press and the control of brick size and density on such a press is essential to an understanding of this invention. The toggle press comprises a mold box with vertical side walls and upper and lower pressure plates which enter the mold box to compress a refractory batch being shaped into brick. The lower pressure plate is supported by a stool fastened to a saddle which seats on a lower crosshead during pressing. The upper pressure plate is connected by toggle arms to an upper crosshead. Joining the upper and lower crossheads are Vertical side arms. These side arms bear a resultant tensile load during pressing.

Control of the weight of the brick or shape being pressed is accomplished by allowing a larger or smaller volume (and, therefore, weight) of a refractory batch to be fed to the mold box. This is accomplished simply by the lower pressure plate during charging of the batch to the mold box. The height of the brick or shape being fabricated is controlled primarily by the distance the upper and lower pressure plates are separated when the toggle is at its straightened position and the saddle is seated on the lower crosshead. The height of the brick is also controlled by the amount of strain in the side bars during pressing.

As the amount of batch fed to the mold box is increased, the brick become heavier. Also, as the batch weight increases, the highth of the brick increases, due to increased strain on the side bars.

It is necessary to adjust the batch weight or charge occasionally during the pressing of a brick batch to maintain uniform density, because as the batch is awaiting to be fed to the mold box it dries, changing the way it Hows. As a result, the same volume of loose batch fed to the mold box does not result in the same weight. Also, it is usually necessary to adjust the feed to the mold box between batches to maintain uniform density, as the flow properties of a fresh batch differ from those of the batch just pressed, and as no two batches compact exactly the same. Determining when to change the charge was traditionally left to the pressmen who occasionally weighed and measured a brick (usually in a haphazard manner). This technique was slow, inaccurate, and unresponsive to sudden changes; for example, when the batch hung up in the charging box a very poor brick was produced, unknown to the pressmen.

Several innovations have been made to automatically detect when the press is making low-density brick and 3,368,254 Patented Feb. 13, 1968 ICC thereafter increase the charge. These have all been based on measuring the strain in the side bars, described above. Theoretically, given the size of the side bars, their modulus of elasticity, and the strain du-ring pressing, the force applied to a brick during pressing can be calculated. This force can be converted into pressure applied to the brick by dividing the force by the surface area of the brick. There is a relationship between forming pressure and density for plastic refractories. The pressuredensity relationship, and therefore the side bar straindensity relationship, is predictable. By measuring the strain on the side bars, the brick density can be checked or even, to some extent, controlled.

In one apparatus for automatic control, shown in United States Patent No. 987,124, an extensometer bar was attached to the side bars of the press. This mechanical device detected the maximum strain in the side bar and indirectly measured pressure applied to brick in the mold box. Because of the relationships already discussed between density, forming pressure, and charge, the density could be continuously corrected. While this technique is not widely used, it has been found satisfactory by some.

Two later developments in the control of toggle presses are reported in United States Patents 2,455,823 and 3,044,139. These are similar to the extensometer technique, except that the maximum strain on the side bars is electrically measured with strain gauges. However, both the strain gauge and extensometer techniques have been found inadequate for controlling the density of nonplastic mixes, since there is a lack of relationship between the maximum strain on the side bars and brick density.

It is therefore an object of this invention to provide a process for making uniform density brick on a toggle press from a nonplastic batch.

lt is a further object of this invention to provide a measuring and control circuit which will measure the maximum pressure applied to brick made from nonplastic batches and inform the press operator of the quality of the brick being manufactured.

This invention is more clearly understood by a study of the attached drawings, in which:

FIG. 1 is a partial cross-section through a typical toggle press used for brickrnaking;

FIG. 2 is a diagram showing the relative positions of the pressure plates during a complete pressing cycle and the corresponding side bar strain throughout that cycle; and

FIG. 3 is a circuit diagram of the measuring and contr-ol circuit.

It was previously surmised that there were two maximum pressures during the pressing cycle caused by the toggle arm being in the straightened position twice. It was also surmised that the pressure on the brick was substantially uniform between the two maximums and would, therefore, cause uniform strain on the side bars. This was found to be the case for plastic mixes. Therefore, the

prior art systems for measuring the strain in the side barsV and relating it to density were adequate for plastic batches.

sponsive to the low voltage signals sent from the strain gauges attached to the side bars. The recorder has an output shaft which turns proportionally to the strain 1n the side bars. The control circuit has a first circuit comprising a normally-open limit switch which is closed when said shaft is turned past a preset position correspondlng to the minimum desirable strain in the side bars. When this limit switch is closed, it energizes an acceptable indicator. A second circuit contains a normally-open limit switch which is closed when the output shaft rotates past a preset position corresponding to the maximum desirable strain in the side bars. This switch energizes a warning indicator. A third circuit contains a normally-closed switch which is operated by a cam that allows the switch to open during that portion of the brickmaking cycle when brick are being ejected from the mold cavity. The third circuit energizes the first and second circuits.

A better understanding of the invention may be had by referring to the drawings in conjunction with the following detailed explanation.

The toggle press A brickmaking toggle press used in the practice of this invention may be such as the well known Boyd-type brick press as shown, for example, in United States Patent No. 987,124. As shown in FIG. l, `the toggle press has a pair of laterally-spaced side frames 1 and 2 between the lower and front part of which a table 3 is rigidly mounted. The table is provided with a rectangular molding cavity 4, which extends completely through it. At the back part of the table, there is a hopper 5 that contains the granular batch to be used in making brick. The lower end of the hopper is spaced from the `table by a charging box 6 which is arranged to slide backward and forward across the molding cavity by means of a rod 7 which is pivotally attached to the rear of the box below its extension 8 and to an arm 9 suspended from a pivot 10 which is mounted across the side frames 1 and 2. The arm 9 is swung back and forth by a link 11 that is pivotally connected to it and to the lower end of an arm 12 which straddles rod 7. The upper end of arm 12 is rigidly mounted on a horizontal rock shaft 13 journaled in the side frames of the machine. The lower end of another arm 14 is rigidly mounted on a projecting end of the rock shaft, and the upper end of this latter arm carries a cam follower roller 15 which travels in the groove of a cam 16 which is mounted on the inner side of a large gear 17. This latter gear is rigidly mounted on a projecting end of a crankshaft 20, the ends of which are, in turn, mounted on bearings 21 carried by the respective side frames 1 and 2. The gear is driven by a pinion 22 on one end of a shaft 23 below it. This shaft 23, likewise, is journaled across the side frames, and its opposite end carries a gear 25 which is driven by a pinion 26 mounted on a shaft 27 behind it. This rear shaft, also, is journaled in the side frames from one of which it projects and carries a pulley 28 which is driven by a belt 29 which is, in turn, interconnected with and driven by an electric motor (not shown in the drawings).

When the charging box 6 filled with granular material is moved across the mold cavity, the material falls into the cavity and fills it, as shown in FIG. l. The material is retained in the cavity by the stool 54 supported by the lower press saddle plate 53 on crosshead 33. The latter is supported at its opposite ends by vertical side bars 34, which have enlarged ends guided through their vertical movements between ribs 35 and 36 on the side frames of the machine. The bars can be moved, vertically, far enough to lift the bottom pressure plate to a level flush with the top of the table.

Journaled in the upper ends of the two side bars is a horizontal shaft 37, also referred to as upper crosshead, on which the upper end of a heavy toggle link 38 is pivotally disposed. The lower end of this link 38 is provided with a central recess, in which the upper end 4 of a lower toggle link 39 is disposed. The adjoining ends of these links are connected by a horizontal shaft 42 on the central portion of which the front end of a crank arm 43 is pivotally mounted. The lower end of the lower toggle link carries a shaft 44, the ends of which are mounted in a middle crosshead 45 that slides up and down the same side frames 1 and 2. This crosshead, 1n turn, carries a plunger 46, which supports a top pressure plate 47 aligned with a mold cavity 4.

The rear end of pitman arm 43 is journaled on the offset center of crankshaft 20. As the large gear 1s rotated, the toggle is straightened and broken by the pitman arm, the bottom of which has cam surfaces 48 that move back and forth across a cam roller 49 which is journaled across the same machine side frames 1 and 2. The action of the press is such that, while the bottom pressure plate 31 is at the bottom of molding cavity 4, the top pressure plate 47 can be raised high enough to permit the charging box 6 to move forward and back beneath it, after which the toggle is straightened out to move the top pressure plate down into the molding cavity to mold a brick. Then the side bars 34 are raised to lift the brick to the top of the cavity, while the toggle and crank arm move thte top pressure plate upward, away from the brick, so that the charging box can again move forward and push the brick forward onto the table in front of the mold cavity.

When the press is in charging position, as shown in FIG. l, the distance between the top of the table 3 and the lower pressure plate 31 can be adjusted. The saddle plate 53 which supports the lower pressure plate 31 through stool 53 is urged up away from the crosshead 33 by spring 59. It is restrained, however, by restoring bar 55 which is in turn held back by lever 56. The fulcrum 57 of lever 56 is attached to crosshead 33 through extension 58. The position of restoring bar 55 during charging can be varied by turning handle 60 and thereby raising or lowering the end of lever 56.

The pressing cycle FIG. 2 graphically shows the relationship between top and bottom pressure plates, the bottom crosshead, and the table level during a complete pressing cycle. FIG. 2 also shows an exemplary strain in the side bars during the critical portion of the cycle when a nonplastic mix is pressed. Twenty-four positions in the pressing cycle have been labeled arbitrarily to aid in description.

At positions P-21 through P-23, the upper pressure plate is clear of the mold box and the lower plate is held at its adjusted level to control the volume of charge. Thereafter, the upper pressure plate lowers into the mold box, and begins to compact the mix. During the compaction, the lower pressure plate is raised in the box slowly towards the table level. Also, during the compaction, the saddle of the lower press pad is seated on the lower crosshead. At about position P-S, the first maximum pressure occurs, because the toggle arms are erect. The pitman arm which pulls the toggle arms into their erect position continues somewhat past the erect position so that at P-6 the pitman arm is at its most rearward position. At a little past P-7, the second maximum pressure occurs. The toggle arms are again erect. Thereafter, the upper and lower pads separate, and the lower pad delivers the brick to the table level for removal.

The strain in the side bars is insignificant until at position P-23 the compaction begins. It reaches its first maximum at about P-5, corresponding to the first maximum pressure on the brick. It is thereafter about the same until it reaches the second maximum pressure, a little past P-7. The second maximum pressure is larger than the first because it is the sum of the strain on the side bars caused by the expanding toggle and an additional strain caused by the force required to eject the brick from the mold box. This is the force required to overcome the friction of the brick on the side walls of the mold box.

Because the irst maximum pressure is related primarily to the strain caused `by the straightening of the toggle and, therefore, the pressure exerted on the shape being formed, it is used to control the brickmaking process. This is accomplished by limiting the control period to between about position P-2 and P-6 of the brickmaking cycle. It is also possible to control during all of the pressing cycles except during the ejection, which is from about P- to P-8.

The control circuit The requirements of the control circuit according to this invention are several. It must inform the pressmen that a low density brick has been made enabling them to discard it. It must also inform the pressmen when brick are consistently being made below the desired density or above the required height-h so that the appropriate adjustments can be made.

Referring to FIG. 3, which is a wiring diagram of the control circuit, A1 and A2 are the active strain gauges attached to the side bars of the press. Their location is shown in FIG. 1 at the center line of the front face of the side bars so that tensile strain only is measured. If positioned elsewhere, bending strain would also be recorded. C1 and C2 are temperature-compensating strain gauges located on the press somewhere near the active gauges or across the active gauge and perpendicular thereto. The gauges are arranged to form the well known Wheatstone bridge circuit for measuring change in resistance. The approximate resistance of the strain gauges is 120 ohms. A constant voltage is applied across points 60 and 61 by the constant voltage source 62 through lead wires 63 and 64. A change in resistance in the active gauges A1 and A2 due to strain causes a change in the output voltage across points 65 and 6'6. This voltage change is measured and recorded by recorder 69 which is connected to the lbridge by lead wires `67 and 68. The recorder is an instrument made by Leeds and Northrup Co., Philadelphia, Pennsylvania, and referred to as a Speedomax H model. Other recorders which are responsive to small voltage changes could be used. A suitable D.C. voltage source is manufactured by Technipower, Inc., Norwalk, Connecticut, referred to as model number M 10.8-0200 A, which has a D.C. output voltage ranging from l0.3-ll.4 volts. The change in the output voltage from the bridge causes an arm 70 within the recorder to rotate. The rotation of the arm is calibrated to measure tons of force applied to the brick. When the arm of the recorder turns past the point corresponding to the minimum acceptance force to obtain good density, a limit switch 71 is tripped which activates the solenoid of a time-delay relay 72 to close switch 73, causing the green acceptable light or indicator 74 to come on.

If the strain on the side bars is too great, the brick will be oversized. Also, there is a possibility of reaching the point where the press will stall or be damage. The oversized brick will cause the recorder arm to turn past the second limit switch 76 which activates the solenoid of another time-delay relay 77. This relay breaks the normally closed switch 7S, cutting out the green light or indicator 74. At the same time, relay 77 closes the normally open switch 79 causing the red warning light or indicator 80 to come on. The time-delay relays are known as on-delay, because after the current to activate their solenoids is removed they remain on temporarily. The delay mechanism contains a synthetic rubber bellows which slowly expands, tripping the relay off when nally expanded. The rate of expansion is controlled by the air orifice to the bellows. The on-delay relays keep the green acceptable light or the red warning light on for several seconds, enabling the pressman to notice them and take the appropriate action.

Because no light comes on if the brick are unacceptable or below density, a white on light 90 is wired to inform the pressman when the control circuit is turned on by switch 91. The pressmen cannot make the error of increasing the charge and pressure to cause the green acceptable light to come on when the control system is turned off.

To prevent the relays 72 and 77 from being actuated by the ejection strain in the side bars, a switch 72 is opened after the first maximum strain, but just prior to the ejection strain thereby de-arming the relays. The switch is operated by a cam 93 which is arranged to turn one revolution for every revolution of a flywheel 17.

Met/10d of controlling brick density The procedure for making brick according to this intion is generally as follows. The upper limit switch, actuated 4by the output shaft of the recorder, is usually set to close when an increase in the tons of force applied to the brick ceases to increase sufficiently the density ofthe brick considering the additional strain to which the press is subjected. The upper limit switch may, however, be set to close at the point corresponding to the force which first causes pressure cracking within the brick. The press is then shimmed until the desired brick thickness is obtained while maintaining the desired force. Thereafter, the lower limit switch is set to be closed whenever a brick of unsatisfactory highth or density is obtained. These lower limits are based on established tolerances well known to the refractories brickmaking industry. The maximum and minimum pressure can, of course, be set without following the procedure detailed above if there is suicient past experience with the particular mix involved. The shimming process must remain a trial and error process due to the mechanical configuration of the press.

While the invention has been described with reference to particular embodiments, it will be understood, of course, that modifications, substitutions, and the like may be made therein without departing from its scope.

Having thus described this invention in detail and with suflcient particularity as to enable those skilled in the art to practice it, what is desired to have protected by Letters Patent is set forth in the following claims.

Iclaim:

1. In combination with a toggle-type brick press having a mold cavity supported by a main frame, upper and lower pressure plates which enter said mold cavity, said upper pressure plate being connected by toggle arms to an upper crosshead, said lower pressure plate fixed above a lower crosshead, said upper and lower crossheads being connected by said bars, a control system comprising resistance strain gauges attached to said side bars, a constant voltage source, means connecting said constant voltage source with said strain gauges, said gauges and constant voltage source arranged to produce an electrical signal proportional to said strain in said side bars, a recorder, means for applying said signal to said recorder, and an output shaft on said recorder which turns proportional to said input signal; a first circuit means comprising a normally open limit switch which is closed when said output shaft is turned past a preset position corresponding to the minimum desirable strain in said side bars, an on-delay relay which is actuated when said switch is closed, closing a switch means energizing an acceptable indicator, a second circuit means containing a normally open limit switch which is closed when said output shaft rotates past a preset position corresponding to a maximum desirable strain in said side bars, an on-delay relay which breaks a normally closed switch de-energizing said acceptable indicator and closing a normally open switch energizing a warning light, a third circuit means containing a normally closed switch which is open during the portion of the brickmaking cycle when brick are being ejected from said mold cavity, said third circuit when closed energizing the first and second circuit means.

2. In combination with a toggle-type brick press having a mold cavity supported by a main frame, upper and lower pressure plates which enter said mold cavity, said upper pressure plate being connected by toggle arms to an upper crosshead, said lower pressure plate xed above a lower crosshead, said upper and lower crossheads being connected by side bars, a control system comprising resistance strain gauges attached to said side bars and a constant voltage source arranged to deliver an electrical signal proportional to the strain to a recorder, there being an Output shaft on said recorder, the improvement comprising a first circuit means comprising a normally open limit switch which is closed when said shaft is turned past a preset position corresponding to the minimum desirable strain in said side bars energizing an acceptable indicator, a second circuit means containing a normally open limit switch which is closed when said output shaft rotates past a preset position corresponding to a maximum desirable strain in said side bars energizing a warning indi- References Cited UNITED STATES PATENTS 2,455,823 12/1948 Tauber et al 25-45 10 3,044,139 7/1962 Morton et al 25-45 3,210,450 10/1965 Bratton 25-90 X I. SPENCER OVERHOLSER, Primary Examiner.

15 J. R. BELL, Assistant Examiner. 

2. IN COMBINATION WITH A TOGGLE-TYPE BRICK PRESS HAVING A MOLD CAVITY SUPPORTED BY A MAIN FRAME, UPPER AND LOWER PRESSURE PLATES WHICH ENTER SAID MOLD CAVITY, SAID UPPER PRESSURE PLATE BEING CONNECTED BY TOGGLE ARMS TO AN UPPER CROSSHEAD, SAID LOWER PRESSURE PLATE FIXED ABOVE A LOWER CROSSHEAD, SAID UPPER AND LOWER CROSSHEADS BEING CONNECTED BY SIDE BARS, A CONTROL SYSTEM COMPRISING RESISTANCE STRAIN GAUGES ATTACHED TO SAID SIDE BARS AND A CONSTANT VOLTAGE SOURCE ARRANGED TO DELIVER AN ELECTRICAL SIGNAL PROPORTIONAL TO THE STRAIN TO A RECORDER, THERE BEING AN OUTPUT SHAFT ON SAID RECORDER, THE IMPROVEMENT COMPRISING A FIRST CIRCUIT MEANS COMPRISING A NORMALLY OPEN LIMIT SWITCH WHICH IS CLOSED WHEN SAID SHAFT IS TURNED PAST A PRESET POSITION CORRESPONDING TO THE MINIMUM DESIRABLE STRAIN IN SAID SIDE BARS ENERGIZING AN ECCEPTABLE INDICATOR, A SECOND CIRCUIT MEANS CONTAINING A NORMALLY OPEN LIMIT SWITCH WHICH IS CLOSED WHEN SAID OUTPUT SHAFT ROTATES PAST A PRESET POSITION CORRESPONDING TO A MAXIMUM DESIRABLE STRAIN IN SAID SIDE BARS ENERGIZING A WARNING INDICATOR, A THIRD CIRCUIT MEANS CONTAINING A NORMALLY CLOSED SWITCH WHICH IS OPEN DURING THE PORTION OF THE BRICKMAKING CYCLE WHEN BRICK ARE BEING EJECTED FROM SAID MOLD CAVITY,A SAID THIRD CIRCUIT WHEN CLOSED ENERGIZING THE FIRST AND SECOND CIRCUIT MEANS. 